L.R. Schaeffer, J. Jamrozik, R. Van Dorp, D.F. Kelton1 and
D.W. Lazenby2
Livest. Prod. Sci. (2000) 65:219-227
Abstract
A multiple regression model was used to derive equations for predicting 24 h milk, fat, and protein yields of dairy cows on either two-times or three-times-a-day milking under different testing schemes. New prediction equations were developed for 72 subclasses of days in milk, parity, and season of calving for each of 18 possible three-times-a-day testing schemes and for each of four possible two-times-a-day testing schemes. The prediction equations were compared to current official factors and found to be slightly better than the official factors. For two-times-a-day testing schemes the accuracies of 14 h fat yield predictions from one milk weight and one fat and protein determination were 0.88 for an evening milking and 0.89 for a morning milking. For three-times-a-day milkings the accuracies of 24 h fat and protein yields from two milk weights with fat and protein contents on each were 0.91-0.94 depending on which two of the three milkings were observed. If only one of three milkings were recorded, then accuracies of 24 h predicted fat and protein yields dropped to 0.80-0.82. More data from herds milking three-times-a-day are needed on all breeds.
Keywords: dairy cattle; daily yields; recording schemes; prediction
1Population Medicine, University of Guelph
2Ontario Dairy Herd Improvement Corporation, Guelph